Kees Cook of the ChromeOS security team discovered a buffer overflow in pam_env, a PAM module to set environment variables through the PAM stack, which allowed the execution of arbitrary code. An additional issue in argument parsing allows denial of service.
The oldstable distribution (lenny) is not affected.
For the stable distribution (squeeze), this problem has been fixed in version 1.1.1-6.1+squeeze1.
For the unstable distribution (sid), this problem will be fixed soon (the impact in sid is limited to denial of service for both issues).
We recommend that you upgrade your pam packages.